The present invention relates to a method for the improvement of the antistatic performance of a shaped article of a synthetic resin or, more particularly, to a method for the improvement of the antistatic performance, i.e. decreasing the surface resistivity and accumulation of static electricity on the surface of a shaped article of a synthetic resin by means of low temperature plasma treatment.
Shaped articles of various kinds of synthetic resins are widely used in a variety of fields not only as a general-purpose product but also for several specific applications because they are manufactured usually with high productivity and outstandingly low costs in addition to their excellent properties such as electric insulation. This desirable property of high electric insulation or, in particular, high surface resistivity, of synthetic resin shaped articles, however, causes several difficult problems due to the accumulation of static electricity on the surface as accompanied by the relatively small dielectric loss thereof. For example, the surface of synthetic resin shaped articles rapidly loses beautifulness in appearance by the deposition of dusts and dirts thereon. Human bodies coming into contact with an electrostatically charged surface of such a shaped article are badly influenced by receiving electric shocks and spark discharges between charged surfaces sometimes causes serious problems of disturbance, i.e. noise generation, in electronic circuits.
Therefore, it is a very important technical problem to develop a convenient and efficient method for the improvement of the antistatic performance of or for the decrease of the accumulation of static electricity on the surface of a synthetic resin shaped article. Various attempts have been made in the prior art in this regard. For example, a synthetic resin to be shaped is compounded with a sufficient amount of an electroconductive particulate material such as a metal powder or carbon black before molding into a shaped article. Surface resistivity of a synthetic resin shaped article can be decreased when provided with a very thin electroconductive film of a metal formed thereon by the techniques of sputtering, vapor deposition or other suitable method. Static electricity on the surface can be decreased by increasing the hydrophilicity of the surface by the use of a surface active agent as an antistatic agent which may be either incorporated into the body of the article by the admixture of the resin therewith prior to molding or applied by coating on the surface of the shaped article. Alternatively, introduction of hydrophilic groups or structure to the surface of a shaped article is also effective to decrease the static electricity as is obtained by a chemical treatment, e.g. acid etching, flame treatment, surface grafting by means of actinic rays such as electron beams, ultraviolet light, ionizing radiations and the like.
These prior art methods are indeed effective to some extent but never satisfactory due to the disadvantages of, for example, insufficient effectiveness in improving the antistatic performance, adverse effects on the characteristics of the shaped article in bulk if it be possible to impart sufficient antistatic performance, extremely high costs for the treatment and applicability of the method limited to relatively small articles or treatment in small quantities.